Positive association between circulating free thyroxine and insulin‐like growth factor I concentrations in euthyroid elderly individuals

Publisher Website
Google Scholar
Abstract
OBJECTIVE Previous studies have shown marked changes in circulating insulin‐like growth factor‐I (IGF‐I) levels in hypo‐ and hyperthyroid patients. In this study we examined whether the circulating concentration of IGF‐I may also be affected by normal thyroid hormone levels. DESIGN A cross‐sectional study of thyroid hormones and plasma IGF components in a population‐based sample. PATIENTS 50–80 year‐old men (n = 262) and women (n = 218) with normal concentrations of serum free thyroxine (f T4), free triiodothyronine (f T3) and thyrotrophin (TSH). MEASUREMENTS Plasma concentrations of IGF‐I, IGF‐II and IGFBP‐3, and serum concentrations of TSH, f T3 and f T4. RESULTS Serum f T4 values were weakly positively correlated and serum TSH levels were inversely correlated with circulating IGF‐I concentrations. The associations persisted after adjustment for age and ideal body weight. CONCLUSIONS Our data demonstrate that thyroid hormones are positively correlated to IGF‐I plasma levels even under physiological conditions. However, thyroid hormones explain only 1–2% of the normal variability of circulating IGF‐I.

This publication has 39 references indexed in Scilit: